Bar-eye  (B)  is  a  dominant X-linked mutation with reduced number of
   facets in the eye (wild type B^+ has about 800 facets).
   Homozygous females show semidominance: a more pronounced phenotype (68
   facets) than heterozygotes (358 facets).
   B^D   (double-Bar)  females  show  even  fewer  facets  (45),  due  to
   triplication of region 16A of the X chromosome.